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Subject: [Bug 209842] backtrace(3) function can return negative
Date: Sun, 29 May 2016 20:45:28 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D209842

            Bug ID: 209842
           Summary: backtrace(3) function can return negative
           Product: Base System
           Version: 10.3-RELEASE
          Hardware: arm
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: misc
          Assignee: freebsd-bugs@FreeBSD.org
          Reporter: phk@FreeBSD.org

The backtrace(3) function returns size_t which is unsigned:

     size_t
     backtrace(void **addrlist, size_t len);

And is documentet as returning:

   RETURN VALUES
     The backtrace() function returns the number of elements that were fill=
ed
     in the backtrace. [...]

The implementation in contrib/libexecinfo/unwind.c clearly knows that the
return value can be all-ones:

        if (ctx.n !=3D (size_t)~0 && ctx.n > 0)
                ctx.arr[--ctx.n] =3D NULL;        /* Skip frame below __sta=
rt */

        return ctx.n;

This happens on a BeagleBoneBlack running

    10.3-STABLE FreeBSD 10.3-STABLE #0 r300092

I am not sure what the proper fix is here, nor for that matter what the pro=
blem
might be that causes it to return the all-ones value in the first place.

But at the very least ctx.n should be slammed to zero before returning it, =
so
the code calling backtrace(3) doesn't run off the end of the world.

--=20
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